DNA Study of Breast Cancer Gives More Answers

A new study shows that certain changes in the patterns of DNA taken from breast cancer tumors may be a better predictor of a patient's prognosis and her response to certain treatments.

The study results join a host of recent findings that suggest the key to thwarting breast cancer may lie in the genetic makeup of the tumor.

The genetic makeup of breast cancer tumors may determine how well a woman will fare better than knowing a tumor's size and appearance.

"Is this going to go into clinical practice tomorrow? No," says Dr. Daniel Silver, at the Dana-Farber Cancer Institute in Boston, Mass. "This is just one step of many toward a deeper understanding of breast cancer."

The study was published in the journal Science Translational Medicine.

New Technology Provides Tools to Learn

A European team of researchers analyzed the genetic makeup of 595 breast cancer tumors and compared the results to non-cancerous breast tissue.

They then used math tools to divide tumors into eight types based on changes in the structure of the chromosomes, including deletions or an increase in the effect of DNA.

Physicians have begun to rely more on findings from the DNA of breast cancer cells to learn which cancers will respond to certain treatments and which ones have the greatest chance of recurrence, explains Dr. Stephen Sener, at the University of Southern California.

"For many years, until about the turn of this century, breast cancer was thought to be one basic disease," explains Dr. Sener. "But since the human genome was elucidated, now people are working on the breast cancer genome. We're learning a lot more about how cancers develop and how they behave."

Instead of size, grade, number of lymph nodes impacted and other anatomical features of the tumor itself, many oncologists now peer at the genetic makeup of the tumor.

DNA technology has already revolutionized oncologists' treatment decisions, says Dr. Sener.

Early Stages of Personalizing Medicine

Already, lab testing can show if cancer cells are estrogen receptor (ER) positive, meaning the cells use estrogen to promote their growth; progesterone receptor (PR) positive; hormone receptor negative; or whether they have too many copies of the HER-2 gene, which promotes cell growth.

For each type, different medications may or may not work. For ER positive cancers, for example, drugs such as tamoxifen that block hormones can be effective, but would not work in women with hormone receptor negative cancers.

"There are some breast cancers that are very large that never spread," notes Dr. Sener.

"On the other hand, there are some patients who have very small cancers who have lots of lymph nodes involved," he says. "Why are those patients different? What a lot us have realized is the standard anatomical descriptions of breast cancer is inadequate.

"This new way of looking at breast cancer genetics has allowed us to be much more focused about the prognosis, who will respond to chemo, hormones, or both," says Dr. Sener. "It's really a major advance in breast cancer technology that has emerged in the last three to five years."

Dr. Sener says that eventually, the size of the tumor will probably be an irrelevant piece of information.

Always consult your physician or other healthcare provider for more information.